1. Field of the Invention
This invention relates in general to wireline instruments for measuring temperature and pressure in oil and gas wells and in particular to a latching mechanism for use with such instruments to prevent upward movement of the instrument in flowing oil and gas wells.
2. Description of the Prior Art
Pressure and temperature measurements are commonly taken downhole in flowing oil and gas wells in order to determine reservoir conditions. A typical manner in which the measurements are taken is by lowering temperature and pressure instruments into the well to a depth slightly abovethe zone desired to be measured. Conductor cable is frequently used to lower the instruments into the well so that a concurrent surface indication is displayed at the surface.
Since a flowing well is under pressure, a sealing apparatus is placed on top of the christmas tree of the type that seals against the internal pressure but allows the line to move. Normally the flow from the well is shut off at the surface while the instrument is being lowered. Because of the pressure, there is a tendency for the cable to be pushed out of the sealing apparatus, thus lead weights are attached to the instrument to cause it to sink. The well is allowed to flow once the tool is at the desired place. In very high flow rate wells, the fluid flow may cause the instrument to move upward, even though sufficient weights were used to lower the instrument into the well. This can cause the cable to knot and kink, making it difficult to retrieve the instrument through the sealing apparatus.